don't allow broken distill library versions

`0.9.3` and `0.9.4` versions of the distill library have bug when
dealing with format chains (see raulfraile/distill#13).

Author: Christian Flothmann

composer.json

@@ -18,7 +18,7 @@
         "guzzlehttp/progress-subscriber": "~1.1",
         "symfony/console": "~2.5",
         "symfony/filesystem": "~2.5",
-        "raulfraile/distill": "~0.9"
+        "raulfraile/distill": "~0.9,!=0.9.3,!=0.9.4"
     },
     "extra": {
         "branch-alias": {